(a) Field of the Invention
The present invention relates to a self-piercing rivet. More particularly, the present invention relates to a self-piercing rivet that can penetrate and join more than two joining objects.
(b) Description of the Related Art
Automotive industries pay attention to environmental problems, and apply aluminum alloy and plastic materials to a vehicle body so as to reduce weight of the vehicle body and to improve fuel consumption being one of solutions that solves the environmental problems.
For these purpose, joining methods for assembling the vehicle body have been researched and developed instead of conventional spot welding.
Recently, a self-piercing rivet using a self-piercing rivet system is increasingly used.
According to a conventional riveting technique, joining objects such as steel sheets are joined by forming a head portion after a riveting hole is bored and a rivet is inserted into the riveting hole. However, the rivet is press-fitted into the joining objects by hydraulic pressure or pneumatic pressure without forming the riveting hole according to self-piercing rivet technique. At this time, the rivet is deformed plastically and joins the joining objects.
A self-piercing rivet is used for joining metal sheets according to the self-piercing rivet technique, and the self-piercing rivet includes a head and a partially hollow cylindrical shank.
For example, a shank of the self-piercing rivet penetrates an upper sheet by a punch of a setting tool. At this time, the shank is supported by a die and is deformed outwardly. In addition, since the shank is press-fitted to a lower sheet in a state that the head portion is supported by the upper sheet, the upper sheet and the lower sheet are joined.
Since the shank of the conventional self-piercing rivet is formed as an annular piercing edge, a penetrated portion of the upper sheet is completely cut off by the annular edge when the shank penetrates the upper sheet and is press-fitted to the lower sheet.
Since the penetrated portion of the upper sheet cut off by the shank cannot form mechanical interlock of the upper and lower sheets and remains as a dead metal, joining strength of the upper and lower sheets may be deteriorated.
In addition, since the dead metal cannot join the upper and lower sheets with sufficient strength, the upper sheet rotates relatively with respect to the lower sheet.
Accordingly, various techniques for preventing rotation of the upper sheet are applied according to conventional arts. For example, a plurality of rivets is used for preventing the rotation of the upper sheet.
If the plurality of rivets is used, processes may be complicated, productivity may be deteriorated, and product cost may be increased due to increase of processes and components.
Since the shank of the rivet is formed as the annular piercing edge, the shank penetrates the upper sheet with an annular shape, and thereby increases joining load according to conventional arts.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.